The present invention is directed to a socket for rotatably supporting a tool in a head housing of a dental handpiece. The socket includes a hollow cylindrical shaft which has a bore for receiving a tool which extends out of one end and has a dog for engagement with a flattened surface on a shank of the tool for transmission of torque therebetween. The socket has a catch means or device including at least one support element which extends parallel to the axis of the hollow cylindrical shaft and has a catch nose extending radially inward for engagement in an annular groove in the shank of the tool disposed in the shaft. The catch device includes a thumb actuated purchase disposed on the head housing for releasing each of the catch noses upon actuation to allow disengagement of the tool from the socket.
A known type of rotatable socket for rotatably supporting a tool in a head housing of dental handpiece is disclosed in British patent specification No. 1,127,453. In this tool, a tubular shaft receives the tool with it extending from one end and opposite that one end, an elongated support lamina or plate is movably mounted on the housing to engage a groove of the tool while in a locked position to prevent axial slippage of the tool from the tubular shaft. This support lamina is connected to a spring loaded slide which can be actuated by the thumb of the operator. For axial removal of the tool, the slide is actuated in a longitudinal direction so that the lamina is moved from the locking position to a released position. In this design, the slide must also be actuated when the tool is introduced into the hollow shaft. This arrangement of the slide, which is movable along the handpiece together with the support lamina represents a rather costly design which increases the size of both the head housing and the neck part of the handpiece. Moreover, constant friction exists between the rotating tool and the slide, which is fixed with respect thereto and therefore this friction will increase wear of both parts.
Another known design of a rotatable socket is disclosed in German O.S. No. 28 22 708. In this design, radially loaded clamping elements in the form of rotatable bodies, which have a concave surface of rotation, are provided for holding the tool in a locked position in a tubular shaft. The rotatable bodies are seated over a part of the circumference around the edges of an annular groove of the tool shank and are held in the locked position either constantly through a constant spring loading or by means of their self resiliency.
The space requirements for the rolling bodies likewise increases the size of the head housing particularly in the axial direction of the housing. If on the basis of work requirements, one proceeds from the fact that the head housing should be as short as possible and as small in diameter as possible, this type of structure would provide a relative small seating length and produce the disadvantage of less excellent bearing guidance for the tool which runs relatively fast. Since the full clamping force, which is required for only holding the tool, must be overcome for the axial removal of said tool, the force required for opening the clamping device, moreover, is relatively great in this design. A removal of the tool is thus only possible by means of a strong pull on the tool by hand or by utilizing a separate drill ejector, which must be inserted through an opening in the upper portion of the housing head. The force to be exerted in order to eject the tool must also be exerted in order to engage the tool.
Another known type of rotatable sockets is disclosed in U.S. Pat. No. 4,014,099. In this device, a hollow sleeve or tubular shaft, which accepts the tool, exhibits a catch nose at its upper end surface facing away from the tool discharge end of the hollow sleeve and the catch nose is engaged in an axial groove so that axial slippage of the tool is prevented. A further projection is provided in the sleeve for torque transmission between the tubular shaft and the tool; however, this projection does not engage the corresponding surfaces of the tool as the tool is inserted but rather only engages the tool when the tool is rotated with respect to the tubular shaft. For removal of the tool, the tool must first be rotated in the tubular shaft to align the tool. Then a specific axial force corresponding to the restraining force must be exerted on the tool to pull it out while the tubular shaft is held fast in order to prevent relative movement between the tubular shaft and the tool during the removal operation. Such requirements are also undesirable.